1. Field of the Invention
The present invention relates to a combined type thin film magnetic head provided with both an inductive magnetic conversion element and a magnetoresistive (hereafter referred to as MR) element.
2. Discussion of Background
A combined type thin film magnetic head of this type employs an inductive magnetic conversion element for a recording element and employs an MR element for a reproduction element. One of the features of such a combined type magnetic head is that, since the reproduction output of the MR element is not dependent upon the speed of the recording medium, high reproduction output can be achieved.
The inductive magnetic conversion element constituting the recording element in a combined type magnetic head is provided with a thin film magnetic circuit comprising a lower magnetic layer, an upper magnetic layer and a coil layer and is positioned on a slider. The front ends of the upper magnetic layer and the lower magnetic layer constitute pole tips which face opposite each other via a gap layer, and the upper magnetic layer and the lower magnetic layer are provided with a back gap portion for completing the thin film magnetic circuit in the rear.
The MR element is provided on the slider under the inductive magnetic conversion element and is positioned between an upper shield layer positioned above it and a lower shield layer positioned below it. Normally, the upper shield layer also functions as the lower magnetic layer of the inductive magnetic conversion element. By absorbing the superfluous magnetic flux that is not required for a read operation, the upper shield layer and the lower shield layer contribute to improving the resolution and the high frequency characteristics and to improving the recording density.
The basic structure of the combined type magnetic head such as described above is disclosed in, for instance, Japanese Unexamined Patent Publication (KOKAI) No. 116009/1990 and Japanese Unexamined Patent Publication (KOKAI) No. 258323/1986.
The MR element employed in a combined type magnetic head includes an MR film and a magnetic domain control film. The MR film may be one that utilizes the anisotropic magnetoresistance effect or the giant magnetoresistance effect, such as a spin valve film structure.
The magnetic domain control film applies magnetic domain control upon the MR film. In other words, it sets the MR film in a state of being a single magnetic domain, to prevent noise (Barkhausen noise) caused by irregular movement of the magnetic domain wall. Normally, the magnetic domain control film is also utilized as a conductive path in itself, or in a state achieved by being laminated with a non-magnetic conductive film.
The inductive magnetic conversion element is laminated onto the MR element achieving a positional relationship whereby the magnetic domain control film and the lower shield layer are positioned below the back gap portion of the upper magnetic layer and the lower magnetic layer.
One of the problems of the combined type magnetic head described above is that since the magnetic domain control film and the lower shield layer are located extremely close to both the lower magnetic layer and the back gap portion in the area under the back gap portion of the upper magnetic layer and the lower magnetic layer, a magnetic circuit passing from the back gap portion through the lower shield layer and the magnetic domain control film is formed parallel to the original magnetic circuit achieved by the lower magnetic layer, resulting in a portion of the recording magnetic flux being leaked to the lower shield layer and the magnetic domain control film. Since this leaked magnetic flux passes through the MR film, it changes the magnetization of the MR film. This change of magnetization dissipates when a specific length of time has elapsed after the recording current is cut off. However, if recording/reproduction is repeated in cycles of shorter duration than this dissipation time, there will be residual magnetization change in the MR film at the time of reproduction, adversely affecting the reproduction output characteristics. The adverse effect of the leaked magnetic field on the reproduction characteristics is manifested as noise, such as, for instance, fluctuation in the reproduction output, asymmetric fluctuation and distorted reproduction waveforms. This problem becomes more pronounced as the lower magnetic layer and the gap layer become thinner.